Fig. 7.

Schematic of mammalian ear canal development. (A) Invagination of the primary canal (asterisk) with a meatal plug (MP) at its tip. (B) Extension of the meatus towards the forming middle ear and selective loss of periderm in the primary canal. (C) Closure of the primary canal and further extension of the meatal plug to reach the tympanic ring (TR). (D) Loricrin expression (red dashed line) marks the site of opening of the canal. Vertical black dashed lines between brown and blue regions in C and D represent the two distinct parts of the ear canal. (E) The whole external ear canal opens, with the upper/rostral wall of the meatal plate forming the outer surface of the ear drum, and the open canal lined by a cornified layer. 1PP, first pharyngeal pouch; MEC, middle ear cavity. Stages in schematics represent approximate age in human embryonic and fetal stages (top line), and in days of embryonic development (E) and postnatal development (P) in the mouse (bottom line).